Suppose f is a function such that f(f(x))=x for all x in the domain of f, and suppose thatf(0)=2003 . Find all roots of the equation f(x)=0
If f( f(x) ) = 0 then f( f(x) ) and f(x) must be inverses; indeed, f(x) must be its own inverse.
Since f(0) = 2003, f(2003) = 0.
f(x) = 2003 - x.
+1836 
